This project focuses on the molecular biology of enveloped viruses which include a broad group of viruses from negative strand viruses (measles, rabies), to retroviruses (AIDS virus), to DNA viruses (herpes virus). The goal of this research is to study the basic molecular mechanisms of viral pathogenesis from viral entry and assembly to viral gene expression and replication. The understanding of these mechanisms will be necessary in a long term to design novel targeted gene delivery systems or gene expression systems with possible applications in gene therapy and vaccine development. Our plan is to develop defective virus particles with tropism for neuronal or nonneuronal cells. So far our studies have centered around vesicular stomatitis virus (VSV) but the basic strategies can be applied to other enveloped viruses. Towards these goals we found that viral assembly and cytopathogenesis of VSV are most likely independent events. We also found that the high affinity of the polymerase protein NS to the defective interfering particle genome determines the level of autointerference. These are important observations for the understanding of viral pathogenesis on one end of the spectrum and the establishment and maintenance of persistent infections on the other end. For the targeting of viruses to specific cells we were able to insert a chimeric HIV receptor CD4-VSV envelope glycoprotein into a majority of VSV particles. These particles could be specifically immunoprecipitated with antibodies to the CD4 protein. We were also able to insert normal human CD4 molecule into the VSV envelope. Experiments are in progress to test whether the efficiency of the insertion as well as viral assembly depend on the presence of the cytoplasmic tail region of the VSV envelope protein. We are in the process of developing a system which allows studying the molecular mechanisms of viral assembly when the viral envelope protein is absent and/or replaced by a recombinant chimeric envelope protein. Using vaccinia virus we were able to express the VSV N, NS and L genes and replicate a defective virus genome in the absence of helper virus. This finding is particularly promising in our efforts to generate the first recombinant rhabdovirus.